Rheumatoid factor (RF) is an antibody, measurable in the blood, which can bind to other antibodies, normal proteins in the human blood that are important parts of our immune system.
It is present in about 80% of adults with rheumatoid arthritis (RA) but it can also be present in patients with other conditions, like:
- Systemic lupus erythematosus
- Infectious hepatitis, syphilis
- Infectious mononucleosis
- Liver disease
Sometimes, the rheumatoid factor can also be present in normal individuals without diseases but this usually occurs in people with family members who have rheumatoid arthritis.
The higher the level of rheumatoid factor, the more severe the rheumatoid disease and tendency to develop non-joint manifestations of rheumatoid diseases, such as rheumatoid nodules and rheumatoid lung disease.